Mounjaro leg pain: What's normal, what's not and when to get help

If you’re taking Mounjaro for weight loss, you might’ve noticed a few pesky side effects cropping up: nausea, constipation, fatigue and diarrhea. You may also be experiencing leg pain – whether it’s a cramp, ache, tingling sensation or discomfort around the injection site.

Whatever the case may be, you’re likely wondering whether leg pain is a normal reaction to Mounjaro or if it’s a cause for concern. Here’s what you should know.

Does Mounjaro cause leg pain?

While leg pain isn’t one of the most common Mounjaro side effects, some users do report it. 

Leg pain can manifest in different ways for different people. In certain cases, it shows up as a muscle or joint ache either in their whole leg or in a specific part, like the knee or calf. In others, it’s persistent cramps, tingling, numbness, or general pain around the injection site. A handful of users also experience pain across other parts of their body, like their shoulders, abdomen and back.

How common is leg pain as a side effect?

Leg pain isn’t frequently listed as a side effect in clinical trials. Instead, most side effects linked to Mounjaro are gastrointestinal – but we’ll explore these further down. 

That said, plenty of anecdotal evidence suggests that muscle, leg and joint pain do happen. Some people find the discomfort goes away after they adjust to the medication, while others notice it persists the entire time they're using Mounjaro.

What the research says about Mounjaro and muscle or nerve pain

There’s very little scientific evidence indicating that Mounjaro can cause muscle or nerve pain, although a few published case reports have emerged recently. 

For instance, one 2025 report presented a 35-year-old woman who developed severe rhabdomyolysis – a serious condition where muscle tissue breaks down – and required hospitalisation [1]. There were no other known causes, and once she stopped taking tirzepatide (Mounjaro), her condition resolved – indicating a potential link. 

Another case report from 2025 presented two men who developed body aches in their neck, shoulder and back, and morning headaches very soon after injecting tirzepatide [2].

The research around Mounjaro side effects outside those reported in trials is still in its early days, but more studies may come out in time.

Why are my legs so painful all of a sudden?

Pain can be a persistent side effect for some users, but others report that it starts quickly, within 24 hours of injecting. If the pain comes on suddenly, it could be due to a reaction at the injection site. Mounjaro is typically injected into the abdomen, upper arm or upper thigh, and some people find that after injecting into their leg, they notice immediate discomfort. 

Other possible explanations are rapid shifts in fluids or electrolyte levels – caused by gastrointestinal side effects – or muscle strain after starting a new exercise regimen.

Other possible causes

Other reasons you might be experiencing leg pain while taking Mounjaro include:

• Dehydration: Mounjaro can cause diarrhea and vomiting, both of which can lead to dehydration. Low fluid levels can then trigger muscle cramps and discomfort
• Low electrolytes: The digestive side effects above can also cause your body to lose electrolytes, which are essential for muscle contraction and nerve function. With fewer electrolytes, you might feel pain in the legs
• Magnesium deficiency: Magnesium helps your muscles relax and your nerves function properly. Mounjaro is designed to decrease your appetite, potentially meaning you’re not consuming enough magnesium-rich foods and possibly putting you at risk of a deficiency
• Increased physical activity: When you start taking Mounjaro, you might rapidly increase your activity levels. This could lead to a muscle strain, or soreness, stiffness or aching as your body adapts
• Rapid weight loss: Losing weight quickly – which can and does happen while taking Mounjaro – can place strain on your muscles and connective tissue, sometimes leading to aches and pains. Significant weight loss also changes your body's centre of gravity, which may also affect how you move and contribute to discomfort. That’s why many people benefit from guided solutions such as the Juniper Programme, which pairs weight loss treatments with lifestyle and nutrition support to minimise side effects and help with sustainable progress on your weight loss journey

Other side effects of Mounjaro

Like most medications, Mounjaro does come with the risk of side effects. Leg pain isn’t one of the most commonly reported, but these are:

• Nausea
• Diarrhea
• Decreased appetite
• Bloating and gas
• Vomiting
• Constipation
• Indigestion and abdominal pain
• Fatigue
• Injection site reactions (pain, swelling, redness, bruising)
• Belching or burping (which can lead to Mounjaro breath)
• Dizziness

For many users, side effects are quite mild and disappear as their body adjusts to the medication. They might crop up again when increasing to a new dose, but often settle when the body adapts.

Rare but serious side effects to watch for

In very rare cases, Mounjaro can cause:

• Allergic reactions like rash, swelling or trouble breathing
• Pancreatitis (severe pancreas inflammation)
• Kidney or gallbladder problems
• Hypoglycemia (low blood sugar)
• Serious gastrointestinal side effects and severe stomach pain
• A possible higher risk of thyroid cancer

If you’re experiencing any of these, reach out to your GP as soon as possible. If you require urgent attention – like if you can’t breathe, you have chest pain, or there’s severe swelling – call 999 straight away.

When leg pain may be linked to another symptom

There’s also a chance your leg pain is entirely unrelated to taking Mounjaro. Be alert if leg pain occurs alongside swelling, redness, warmth, numbness or shortness of breath, as these may indicate other conditions like deep vein thrombosis (DVT) or infection.

When to speak to your health practitioner

If you notice any of these symptoms, make an appointment with your GP as soon as possible:

• Leg pain that lasts several days with no improvement
• Pain that gets in the way of normal activities like walking and standing
• Redness, swelling, warmth, numbness, tingling or weakness alongside the pain
• Pain that's sudden and intense
• You’ve got an underlying condition like diabetes or heart disease

Red flag symptoms that need urgent attention

Some symptoms require immediate attention. Call 999 straight away if you’re dealing with acute pain alongside:

• Shortness of breath, chest pain or palpitations
• Infection (redness that spreads, fever, pus or warmth)
• Sudden inability to move your leg
• Significant swelling

What to tell your practitioner to get the right support

When you meet with your GP or healthcare practitioner, you should run through when the pain came on, its severity, location and duration. You should also mention any other symptoms you’re experiencing to see if they’re related to the medication or something else. 

Your doctor will likely review your Mounjaro dose and other medications you’re on, as well as lifestyle factors like exercise changes, nutritional deficiencies and hydration that could be contributing to the pain. They may also conduct blood tests to see if there are any signs of other issues, like electrolyte imbalance or magnesium deficiency.

Tips for managing leg pain on Mounjaro

If you’re noticing leg pain, there are a few things you can do to try and relieve it.

At-home remedies and self-care

For mild cases, home remedies may be enough. You could try:

• Boosting your hydration: Drink plenty of water throughout the day, especially if you’re experiencing digestive side effects like vomiting or diarrhea. Consider an electrolyte drink if you need to restore the balance
• A magnesium supplement: If you’re not getting enough magnesium via your diet, look into taking an oral supplement to increase your magnesium levels. It’s usually best to chat to your doctor before trying a new supplement
• Upping your protein intake: Protein supports muscle repair, so try to include lots of protein-rich foods in your diet – think lean meats, eggs, dairy, beans and tofu
• Stretching and gentle movement: Light stretching, yoga and short walks can help relieve muscle pain and stiffness. If you’re finding that moderate-intensity exercise makes the pain worse, consider switching to more gentle activities such as walking or swimming
• Hot and cold therapy: Warm compresses are great for muscle aches and pains, while ice packs can help with inflammation and acute pain
• Pain relief: Try a non-prescription painkiller, such as ibuprofen or paracetamol, or a topical cream like menthol gel
• Rotating your injection site: If injecting Mounjaro into your thigh causes discomfort, make sure to rotate your injection site regularly. Experts recommend using a new site each week

Adjusting dose or timing with medical guidance

If at-home remedies aren’t working, your doctor might suggest certain treatments to address your leg pain, like prescription pain relief or muscle relaxants. 

As for the medication itself, they may also suggest lowering your dose or delaying your dose increase until symptoms improve. The timing of your doses can play a role, too; sticking with the same day each week can make your side effect pattern more predictable and manageable. Your doctor might help you figure out an optimal time each week that works for your schedule and allows you to comfortably handle any adverse effects.

If the pain is extreme or doesn’t go away, they may also recommend pausing or discontinuing Mounjaro entirely. For some users, this is the only solution that works.

When switching medications might be considered

Some users tolerate other GLP-1 medications like Wegovy and Saxenda, which have different active ingredients, better than Mounjaro. If the side effects, including leg pain, are persistent or severe and don’t improve with dose or timing adjustments, your doctor may suggest transitioning to other weight loss medications.

If your doctor recommends making the switch, they’ll develop a tapering plan to gradually top Mounjaro and introduce a different type of weight loss injection.

If you're thinking about switching from Mounjaro to Wegovy, the good news is that it's both safe and straightforward.

When making the switch, Juniper patients don’t need to restart at the lowest dose. If clinically appropriate, they can continue at a higher dose aligned with recent treatment history. Plus, our switching protocol has only a 7-day gap between medications, compared to 28 days with most other providers.

Juniper’s clinical switching protocol is designed to make the change simple and safe:

• Review — Your clinician assesses your treatment history and dose tolerance.
• Match — If eligible, you start on an equivalent high dose to avoid losing progress.
• Transition — Only a 7-day window is required between your last Mounjaro dose and your first Wegovy dose (most providers require 28 days).
• Support — Pharmacist check-ins, dose adjustments, and lifestyle guidance keep you on track.

Start your Wegovy switch today →

‍

Image credit: Pexels